We report on the characterization of V-defects in GaN-based heterostructures via scanning force microscopy techniques.
The diameter and density of the V-defects are found to strongly depend on growth thickness and temperature of the top
layer, respectively, while no correlation between the V-defect formation and the type of doping could be identified.
Kelvin probe force microscopy measurements revealed for both, n- and p-doped GaN top layers, a decrease of the Kelvin
voltage within the V-defects, which indicates an enhanced work function of the facets of the V-defects with respect to
the planar surface. Surprisingly, an increase of the current flow within the V-defects is found by conductive atomic force
microscopy in case of the n-doped top layer, while current flow into the V-defect is suppressed for the p-doped top layer.
For a consistent explanation of these results we suggest a model, which is based on an enhanced electron affinity of the
{10-11}-surfaces within the V-defects as compared to the planar (0001)-surface.
We demonstrate the potential of Kelvin Probe Force Microscopy (KPFM) for analyzing degradation effects in GaN-based
laser diodes (LDs). Thereby, the surface potential at the mirror facet was measured locally for both, unbiased LDs
and LDs exposed to a well-defined current. In the unbiased case, our KPFM measurements demonstrate the impact of
aging on the mirror facet, which we attribute to a photon enhanced facet oxidation. In case of an externally applied
voltage, the local variation of the Kelvin voltage across the heterostructure layer sequence is analyzed. A clear
correlation between macroscopic I-V-characteristics and the microscopic data obtained with the KPFM is found.
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